The necessity for high performance metallic alloys has increased within the past few years. For example, electronic devices require alloys which possess certain desirable characteristics such as high strength, high electrical conductivity, lightness, high temperature oxidation resistance, high thermal stability, etc. In order to obtain these high performance alloys, it is necessary to combine the metallic components in such a manner so as to provide the desirable traits to the finished product.
In this respect, various techniques have been employed to produce the desired alloys. For example, beryllium-copper alloys find a wide variety of use in electronic devices due to their combination of properties. However, in machining these alloys to their desired shape or form, toxic beryllia containing dust is emitted during the production and machining which is hazardous in an environmental sense and is very difficult to handle. Therefore, this emission of toxic dust represents a distinct disadvantage attendant to the use of such an alloy. Additionally, the precipitate hardening particles which are present in the beryllium-copper alloy have only marginal thermal stability and will coarsen when the alloy is heated above a temperature of about 400.degree. C. This will cause the alloy to lose its desired properties if it is utilized at or above this temperature. Conventional processing methods such as casting possess certain disadvantages which will prevent the production of a wide variety of desired alloy combinations. For example, a particular disadvantage which is present when casting many alloys is that the alloys are plagued with massive segregation of the alloys. Once this segregation occurs, further refinement of the structure is not possible. Therefore, the most beneficial properties cannot be utilized. Another disadvantage which is found when employing a conventional casting technique is that in addition to a large scale segregation during the cooling, it is also possible that uncontrolled precipitation will occur. In the more conventional precipitation-hardened alloys, a high temperature solution annealing step is used to refine the structure of the alloy. A secondary heat-treatment is then required to produce the dispersed precipitates. Therefore, these are additional steps which are required to obtain the desired product. These solution annealed and heat-treated alloys generally do not have good high temperature properties because high temperatures cause the dispersed phase to go back into solution or substantially coarsen.
Several known patents are directed to various methods for preparing metal alloys. For example, U.S. Pat. No. 4,297,135 teaches the addition of borides, carbides and silicides into various metals such as iron, cobalt, nickel or chromium. However, fine binary boride particles of these metals as well as carbides and silicides alone have a low stability at high temperatures so that they grow to sizes too large to effectively strengthen the alloy, and therefore the resultant alloys possess less than an optimum high temperature property. In addition to this, the metals with very large particles per se are initially brittle and therefore cannot be utilized without a subsequent heat treatment. In U.S. Pat. No. 4,436,560, a method is disclosed for dispersing fine boride particles near the surface of the material. Inasmuch as the mechanical properties of an alloy are a function of the bulk of the material, the method which is disclosed in this patent would not result in the production of high strength alloys. Likewise, in U.S. Pat. No. 4,437,890, a method is disclosed which utilizes a relatively small amount of boron to supress copper growth during the sintering step of the process. The small amounts of boron which are utilized would not be sufficient to form the dispersed strengthening particles which the intermetallic compounds of the present invention impart to the finished alloy.
In U.S. Pat. No. 4,439,236, a process is disclosed for the addition of boron into alloys which contain a minimum of 30 atomic percent of at least two metals selected from the group consisting of iron, cobalt and nickel. The large addition of boron into these alloys would result in imparting desirable properties to the alloys at low temperature. It is to be noted that the borides of iron, cobalt and nickel possess only marginal high temperature stability, and therefore these alloys would not posess such desirable properties as high strength at high temperatures. The large amount of borides in these alloys would also substantially reduce ductility making the alloys difficult to process. U.S. Pat. No. 4,439,247 discloses a method which teaches the addition of small amounts of chromium and tin into copper to produce a high strength, high electrical conductivity copper. However, the alloy thus produced would require a series of hot working, cold working and age hardening steps prior to use. It is readily understandable that the necessity for employing these steps would be highly undesirable in a process to obtain an alloy which possesses desirable characteristics. Tin is also highly soluble in solid copper so that even small amounts would have a negative effect on electrical conductivity. Japanese Pat. No. 156743 discloses the internal oxidation of silicon and/or germanium metals in silver to produce stable oxide dispersoids. Inasmuch as the oxygen has to diffuse in from the surface of the particle, the oxide dispersoids are mostly concentrated near the surface thereof. The oxide particles are very difficult to disperse in an even and uniform manner throughout the alloy, and thus the resultant alloy would possess inhomogeneous regions or dispersions which would impart variations of properties in the alloy, these variations not being desirable characteristics for the alloy.
Another U.S. Patent namely U.S. Pat. No. 3,194,656, also relates to a method of making composite articles such as alloys. However, this patent refers to the fact that at least one of the ingredients in the alloy possesses a liquidus temperature which is substantially below that of the matrix metal and thus would limit the ingredients in the composite article to mostly eutectic systems. Also, this patent refers to the high melting compound elements reacting in the liquid and thus are held to the formation sites. Because of high diffusion rates in the liquid, these nucleation sites are normally widely spaced thus forming particles which are too large to effectively strengthen the alloy. In addition, by stating that the liquidus temperature is substantially below that of the matrix metal, it would suggest that even shallow eutectics would also be eliminated. Furthermore, this patent does not address the solubility into molten matrix of the elemental components which are added to form the compound. Many alloying components can not be kept dispersed by holding at temperatures below the matrix. Likewise, this patent further states that the high melting point compound must be a combination of a metal and a non-metal. Also, this patent does not address the kinetics of the reaction. Once the mix is begun, a high reaction rate will prevent further mixing, thus preventing homogeneous castings.
In contradistinction to this patent, the present invention, as will be shown in the following specification, does not limit the ingredients of the alloy to those systems which have a lower melting temperature and therefore peritectic systems are acceptable. Furthermore, it has now been discovered that a low solubility of both elemental components in the solid matrix is beneficial for the reaction to occur. One advantage of this low solubility of the elemental components is that it forces the additions out of solution.
As will hereinafter be shown in greater detail, it has now been discovered that by utilizing certain metallic components which possess certain characteristics, it is possible to obtain metallic alloys which may be designated as high performance alloys due to the fact that they possess highly desirable characteristics of the type hereinbefore set forth such as high strength, conductivity, lightness, thermal stability, etc. In addition, the intermetallic particles will not agglomerate and will remain in the desired particle size and will be uniformly distributed through the matrix material after admixture.